1. Give the definition of Immunology; What are the differences between innate (non-specific) and adaptive (specific) immunity?

Immunology is the study of our protection from foreign macromolecules or invading organisms and  our responses to them. These invaders include viruses, bacteria, protozoa or even larger parasites. In addition, we develop immune responses against our own proteins (and other molecules) in autoimmunity and against our own aberrant cells in tumor immunity. 

Our first line of defense against foreign organisms are barrier tissues such as the skin that stop the entry of organism into our bodies. If, however, these barrier layers are penetrated, the body contains cells that respond rapidly to the presence of the invader. These cells include macrophages and neutrophils that engulf foreign organisms and kill them without the need for antibodies. Immediate challenge also comes from soluble molecules that deprive the invading organism of essential nutrients (such as iron) and from certain molecules that are found on the surfaces of epithelia, in secretions (such as tears and saliva) and in the blood stream. This form of immunity is the innate or non-specific immune system that is continually ready to respond to invasion.  

A second line of defense is the specific or adaptive immune system which may take days to respond to a primary invasion (that is infection by an organism that has not hitherto been seen). In the specific immune system, we see the production of antibodies (soluble proteins that bind to foreign antigens) and cell-mediated responses in which specific cells recognize foreign pathogens and destroy them. In the case of viruses or tumors, this response is also vital to the recognition and destruction of virally-infected or tumorigenic cells. The response to a second round of infection is often more rapid than to the primary infection because of the activation of memory B and T cells. We shall see how cells of the immune system interact with one another by a variety of signal molecules so that a coordinated response may be mounted. These signals may be proteins such as lymphokines which are produced by cells of the lymphoid system, cytokines and chemokines that are produced by other cells in an immune response,  and which stimulate cells of the immune system. 

The immune system is typically divided into two categories--innate and adaptive--although these distinctions are not mutually exclusive.

Innate immunity

Innate immunity refers to nonspecific defense mechanisms that come into play immediately or within hours of an antigen's appearance in the body. These mechanisms include physical barriers such as skin, chemicals in the blood, and immune system cells that attack foreign cells in the body. The innate immune response is activated by chemical properties of the antigen.

Adaptive immunity

Adaptive immunity refers to antigen-specific immune response. The adaptive immune response is more complex than the innate. The antigen first must be processed and recognized. Once an antigen has been recognized, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. Adaptive immunity also includes a "memory" that makes future responses against a specific antigen more efficient.

2. What types acquired immunity do you know?

Active Immunity

Antibodies are produced by the body in response to infection

Naturally Acquired Active Immunity

Antibodies are formed in the prescence of active infection in body - Duration: lifelong

Artificially Acquired Active Immunity

Antigens (vaccines/toxoids) are administered to the person to stimulate antibody production - Duration: many years

Passive Immunity

Antibodies are produced by another source, animal or human

Naturally Acquired Passive Immunity

Antibodies are transferred naturally from an immune mother to her baby through breast milk/placenta - Duration: 6 mos to 1 yr

Artificially Acquired Immunity

Immune serum (antibody) from another human/animal is injected - Duration: 2-3 wks.

3. Give the characteristic of antigen-presenting cells; Recognize the significance of the immune system in combating infection and disease;

An antigen-presenting cell (APC) or accessory cell is a cell that displays foreign antigens complexed with major histocompatibility complexes (MHCs) on their surfaces; this process is known as antigen presentation. T-cells may recognize these complexes using their T-cell receptors (TCRs). These cellsprocess antigens and present them to T-cells.

Antigen-presenting cells fall into two categories: professional and non-professional.

T cells cannot recognize, and therefore cannot respond to, 'free' antigen. T cells can only 'see' an antigen that has been processed and presented by cells via carrier molecules like MHC and CD1 molecules. Most cells in the body can present antigen to CD8⁺ T cells via MHC class I molecules and, thus, act as "APCs"; however, the term is often limited to specialized cells that can prime T cells (i.e., activate a T cell that has not been exposed to antigen, termed a naive T cell). These cells, in general, express MHC class II as well as MHC class I molecules, and can stimulate CD4⁺ ("helper") T cells as well as CD8⁺ ("cytotoxic") T cells, respectively.

To help distinguish between the two types of APCs, those that express MHC class II molecules are often called professional antigen-presenting cells.